withdrawal reflex

reflex

(re'fleks?) [L. reflexus, bending back]

An involuntary response or action to a stimulus. Reflexes are specific and predictable and are usually purposeful and adaptive. They depend on an intact neural pathway between the stimulation point and a responding organ. This pathway is called the reflex arc. In a simple reflex this includes a sensory receptor, afferent or sensory neuron, reflex center in the brain or spinal cord, one or more efferent neurons, and an effector organ. Most reflexes, however, are more complicated and include internuncial or associative neurons intercalated between afferent and efferent neurons. See: reflex arc for illus

abdominal reflex

Contraction of the muscles of the abdominal wall when the overlying skin is stimulated. Absence of this reflex indicates damage to the pyramidal tract.

abdominocardiac reflex

A change in heart rate, usually a slowing, resulting from mechanical stimulation of abdominal viscera.

accommodation reflex

Any of the changes that take place as the eye adjusts to bring light rays from an object to focus on the retina. This involves a change in the size of the pupil, convergence or divergence of the eyes, and either a decrease or an increase in the convexity of the lens depending on the previous condition of the lens. Synonym: near reflex

Achilles tendon reflex

Achilles reflex

acoustic blink reflex

Involuntary closure of the eyelids after exposure to a sharp, sudden noise. This is a normal startle response that may be exaggerated in patients with anxiety disorders or hyperacusis. It may be blunted in infants or adults with a hearing disorder or facial nerve paralysis.

acquired reflex

acromial reflex

Flexion of the forearm and internal rotation of the hand as a result of a quick blow to the acromion. It is elicited in hyperreflexic states.

adductor reflex

Contraction of the adductor muscles of the thigh on applying pressure to or tapping the medial surface of the thigh or knee.

allied reflex

Any of the reflexes initiated by several stimuli originating in widely separated receptors whose impulses follow the final common path to the effector organ and reinforce one another.

anal reflex

Contraction of the anal sphincter following irritation or stimulation of the skin around the anus. This reflex is lost if the second to fourth sacral nerves are injured. Synonym: anal wink

ankle clonus reflex

A reflex elicited by quick, vigorous dorsiflexion of the foot while the knee is held in a flexed position, resulting in repeated clonic movement of the foot as long as it is maintained in dorsiflexion. In women with pregnancy-induced hypertension, this reflects hyperirritability of the central nervous system and increased risk for eclamptic convulsions.

auriculocervical nerve reflex

auriculopalpebral reflex

autonomic reflex

Any reflex involving the response of a visceral effector (cardiac muscle, smooth muscle, or gland). Such reflexes always involve two efferent neurons (preganglionic and postganglionic).

axon reflex

A reflex that does not involve a complete reflex arc and hence is not a true reflex. Its afferent and efferent limbs are branches of a single nerve fiber, the axon (axon-like dendrite) of a sensory neuron. An example is vasodilation resulting from stimulation of the skin.

Babinski reflex

Bainbridge reflex

Bechterew reflex

biceps reflex

Flexion of the forearm on percussion of the tendon of the biceps brachii.

blink reflex

Sudden closing of the eyelids in response to turning of the head, loud noises, bright lights, or visual threats. Absence of this reflex occurs in blindness and in injuries to cranial nerves III, V, and VII.

Brissaud reflex

bulbocavernosus reflex

bulbomimic reflex

bulbospongiosus reflex

Contraction of bulbospongiosus muscle on percussing the dorsum of the penis.

cardiac reflex

An involuntary response consisting of a change in cardiac rate. Stimulation of sensory nerve endings in the wall of the carotid sinus by increased arterial blood pressure reflexively slows the heart (Marey law). Stimulation of vagus fibers in the right side of the heart by increased venous return reflexively increases the heart rate (Bainbridge reflex).

cardiovascular reflex

1. A sympathetic increase in heart rate when there is increased pressure in or distention of great veins.

2. Reflex vasoconstriction resulting from reduced venous pressure.

carotid sinus reflex

A slowing of the heart rate and a fall in blood pressure when the carotid sinus is massaged. Carotid sinus massage may be used therapeutically to treat paroxysmal supraventricular tachycardia.

cat's eye reflex

In children, an abnormal pupillary flash or reflection from the eye that may be momentary; may be white, yellow, or pink; and is best seen under diminished natural illumination. This reflex, which may be noticed first by a parent, may be caused by various conditions, the most important of which is retinoblastoma. It is also observed in tuberous sclerosis, inflammatory eye diseases, and some congenital malformations of the eye.

conjunctival reflex

consensual reflex

consensual light reflex

The reaction of both pupils that occurs when one eye is exposed to a greater intensity of light than the other. See: pupillary reflex

contralateral reflex

1. Passive flexion of one part following flexion of another.

2. Passive flexion of one leg, causing similar movement of the opposite leg.

convulsive reflex

A reflex induced by a weak stimulus and causing widespread uncoordinated and purposeless muscle contractions, seen in strychnine poisoning.

corneal reflex

Closure of eyelids resulting from direct corneal irritation. This reflex is mediated by the fifth cranial nerve.

Synonym: lid reflex

corneomandibular reflex

Deflexion of the mandible toward the opposite side when the cornea is irritated while the mouth is open and relaxed.

cranial reflex

Any reflex whose origin is in the brain.

cremasteric reflex

Retraction of the testis when the skin is stroked on the inner front side of the thigh.

crossed reflex

A reflex in which stimulation of one side of the body results in response on the opposite side. Synonym: consensual reflex; indirect reflex

crossed extension reflex

An extension of the lower extremity on the opposite side when a painful stimulus is applied to the skin.

cry reflex

1. The normal ability of an infant to cry. It is not usually present in premature infants.

2. The spontaneous crying by infants during sleep.

dartos muscle reflex

A wormlike contraction of the dartos muscle after a sudden application of cold to the perineum. When the dartos muscle fibers contract, the scrotal skin becomes wrinkled and is held close to the testes

deep reflex

deep tendon reflex

Abbreviation: DTR

An automatic motor response elicited by stimulating stretch receptors in subcutaneous tissues surrounding joints and tendons. The assessment of DTRs is typically made by striking a tendon (such as the Achilles or brachioradialis tendons) with a weighted hammer. Brisk or hyperactive responses are seen in conditions such as hyperthyroidism, stroke, preeclampsia, or spastic disorders. Diminished responses may be seen in patients with hypothyroidism, drug intoxication, and flaccid neuromuscular disorders. Synonym: deep reflex; muscle stretch reflex See: clonus; knee-jerk reflex

defense reflex

Retraction or tension in response to an action or threatened action.

delayed reflex

A reflex that does not occur until several seconds after the application of a stimulus.

depressor reflex

A reflex that results in slowed muscle activity, as in the heart rate.

digital reflex

Sudden flexion of the terminal phalanx of a finger or thumb when the nail is suddenly tapped.

direct reflex

A reflex in which response occurs on the same side as the stimulus.

direct light reflex

Prompt contraction of the sphincter of the iris when light entering through the pupil strikes the retina.

diving reflex

Slowing of the heart rate when a person's head is immersed in water. This reflex helps to protect a person from drowning, esp. in cold water.

gastroileac reflex

Gault reflex

Geigel reflex

Gifford reflex

glabellar reflex

Blinking of the eyes when the forehead just above the bridge of the nose is tapped. In most people, blinking stops after a few taps on the forehead. If it does not, significant brain disease may be present, e.g., Parkinson disease or any disease that causes frontal lobe atrophy.

gluteal reflex

Contraction of the gluteal muscles from stimulation of the overlying skin.

Gordon reflex

grasp reflex

The grasping reaction of the fingers and toes when they are stimulated. This reflex is normal in the newborn but disappears as the nervous system matures. It may reappear later in life if a person suffers an injury to the frontal lobes of the brain.

Kocher reflex

labyrinthine righting reflex

A reflex, esp. a postural reflex, resulting from stimulation of receptors in the semicircular ducts, utricle, and saccule of the inner ear. This reflex helps orient the head in space and to the rest of the body.

lacrimal reflex

Landau reflex

laryngeal reflex

Coughing from irritation of the larynx or fauces.

laughter reflex

Uncontrollable laughter resulting from tickling or the fear of tickling.

letdown reflex

The movement of breast milk from the alveoli into the lactiferous ducts in response to oxytocin-stimulated contractions. The reflex may be stimulated by suckling or by an infant's crying. Stimulation of the nipple increases the secretion of oxytocin. This technique may be used to stimulate contraction of the postpartum uterus.

lumbar reflex

Lust reflex

Magnus-de Kleijn reflex

In decerebrate rigidity, extension of the limbs on the side to which the chin is turned by rotating the head. There is flexion of the limbs on the opposite side.

mandibular reflex

Clonic movement resulting from percussing or stroking the lower jaw.

mass reflex

Autonomic dysfunction that may occur as a late consequence of transection of the spinal cord. It is marked by episodes of sweating, bradycardia, hypotension, urinary incontinence, and muscular spasms of the legs.

Onanoff reflex

optical blink reflex

Involuntary closure of the eyelids after exposure to a bright light. Shining a bright light at an infant's eyes causes the eyes to blink and the head to flex backward. If this reflex is absent, further testing of cranial nerves II, III, IV, and VI is required.

optical righting reflex

palatal reflex

Swallowing induced by stimulation of the soft palate.

palmar grasp reflex

A normal reflex in a the newborn in which the baby's fingers spontaneously curl around any object placed within them and do not spontaneously let go. This reflex usually diminishes by age 3 to 4 months and disappears before age 6 months. The reflex reappears later in life in diseases that affect the frontal lobes of the brain.

palmar reflex

Swallowing induced by stimulation of the soft palate.

palmomental reflex

A contraction of the superficial muscles of the eye and chin produced on the same side as the palmar area that is stimulated by an examiner. This is an abnormal finding and indicates frontal disease.

parachute reflex

Extension of an infant's arms, hands, and fingers when the infant is suspended in the prone position and dropped a short distance onto a soft surface. This reaction appears at age 9 months and persists. An asymmetrical response indicates a motor nerve abnormality.

pharyngeal reflex

pilomotor reflex

Piltz reflex

placing reflex

Flexion and then extension of an infant's leg that occurs when the infant is held erect and the dorsum of one foot is dragged along the underedge of a table top. This reflex lasts from birth until age 6 weeks.

radial reflex

rectal reflex

red eye reflex

red reflex

The red light reflection seen in ophthalmoscopic examination of the eye.

Synonym: red eye reflex

righting reflex

Any of the reflexes that enable an animal to maintain its body in a definite relationship to its head and thus maintain its body right side up.

rooting reflex

The turning of an infant's mouth toward the stimulus when the infant's cheek is stroked. This reflex is present at birth; by age 4 months it is gone when the infant is awake; by age 7 months it is gone when the infant is asleep.

simple reflex

Snellen reflex

solar sneeze reflex

A sneeze following exposure to bright sunlight. This reflex is and affects a great number of normal people; it may also be associated with rhinitis. The mechanism of the cause of this type of sneeze reflex is unknown.

sole reflex

somatic reflex

spinal reflex

startle reflex

static reflex

A reflex concerned with establishing and maintaining posture when the body is at rest.

statokinetic reflex

A reflex that occurs when the body is moving.

stepping reflex

Movements of progression elicited by holding an infant upright, inclined forward, and touching the soles of the feet to a flat surface. This reflex lasts from birth to age 6 weeks.

stretch reflex

The contraction of a muscle caused by quick stretching of that muscle. Stretch reflexes are of primary importance in the maintenance of posture.

Synonym: myotatic reflex

sucking reflex

A sucking movement of an infant's mouth produced by stroking the lips. A primitive form of this reflex is present in the fetus by the 16th week of gestation; it is fully developed by the time of birth. In adults, the presence of a sucking reflex is an indicator of severe dementia, frontal lobe disease, or extrapyramidal diseases.

superficial reflex

A cutaneous reflex caused by irritation of the skin or of areas that depend on the spinal cord as a motor center (such as the scapular, epigastric, and plantar reflexes) or on centers in the medulla (such as the conjunctival, pupillary, and palatal reflexes). This reflex is induced by a very light stimulus, e.g., stroking the skin lightly with a soft cotton swab.

supraorbital reflex

suprapubic reflex

Deflection of the linea alba toward the stroked side when the abdomen is stroked above the inguinal ligament.

swallowing reflex

Involuntary muscular activity in the oropharynx and nasopharynx when foods, tongue depressors, or other objects stimulate the back of the throat. This reflex is mediated by the deglutition center of the medulla oblongata, i.e., by cranial nerves VII, IX, X, and XI.

symmetrical tonic neck reflex

In an infant, flexion or extension of the arms in response to flexion and extension, respectively, of the neck.

tendon reflex

A deep reflex obtained by sharply tapping the skin over the tendon of a muscle. It is exaggerated in upper neuron disease and diminished or lost in lower neuron disease.

testis compression reflex

Contraction of abdominal muscles following moderate compression of a testis.

tibioadductor reflex

tonic labyrinthine reflex

tonic neck reflex

The ipsilateral extension and contralateral flexion of the supine infant's extremities when the head is turned to one side. This normal newborn reflex may not be evident immediately after birth; however, once it appears, it persists until about the third postnatal month. Synonym: fencing reflex

tonic vibration reflex

Abbreviation: TVR

A polysynaptic reflex believed to depend on spinal and supraspinal pathways.

triceps reflex

Sharp extension of the forearm resulting from tapping of the triceps tendon while the arm is held loosely in a bent position. Synonym: elbow jerk; elbow reflex

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